Extensions of adaptive slope-seeking for active flow control

Henning, Lars; Becker, Ralf; Feuerbach, G.; Muminovic, Rifet; King, Rudibert; Brunn, A.; Nitsche, W.

doi:10.1243/09596518jsce490

Cited by 43 publications

(21 citation statements)

References 32 publications

(60 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…While some flow control methods such as extremum seeking (Henning et al 2008) and machine learning control (Gautier et al 2015) are model free, many more rely on having a mathematical model, and often a linear model, of the fluid system. For example, black-box linear models have often been used for convectively unstable flows such as the backward-facing step (Barbagallo et Modelling and feedback control of bistability in a turbulent bluff body wake 729 flows behave like a linear amplifier, thus allowing linear models to be obtained for various input-output behaviours.…”

Section: R D Brackston and Othersmentioning

confidence: 99%

Stochastic modelling and feedback control of bistability in a turbulent bluff body wake

et al. 2016

View full text Add to dashboard Cite

A specific feature of three-dimensional bluff body wakes, flow bistability, is a subject of particular recent interest. This feature consists of a random flipping of the wake between two asymmetric configurations and is believed to contribute to the pressure drag of many bluff bodies. In this study we apply the modelling approach recently suggested for axisymmetric bodies by Rigas et al. (J. Fluid Mech., vol. 778, 2015, R2) to the reflectional symmetry-breaking modes of a rectilinear bluff body wake. We demonstrate the validity of the model and its Reynolds number independence through time-resolved base pressure measurements of the natural wake. Further, oscillating flaps are used to investigate the dynamics and time scales of the instability associated with the flipping process, demonstrating that they are largely independent of Reynolds number. The modelling approach is then used to design a feedback controller that uses the flaps to suppress the symmetry-breaking modes. The controller is successful, leading to a suppression of the bistability of the wake, with concomitant reductions in both lateral and streamwise forces. Importantly, the controller is found to be efficient, the actuator requiring only 24 % of the aerodynamic power saving. The controller therefore provides a key demonstration of efficient feedback control used to reduce the drag of a high-Reynolds-number three-dimensional bluff body. Furthermore, the results suggest that suppression of large-scale structures is a fundamentally efficient approach for bluff body drag reduction.

show abstract

Section: R D Brackston and Othersmentioning

confidence: 99%

Stochastic modelling and feedback control of bistability in a turbulent bluff body wake

et al. 2016

View full text Add to dashboard Cite

show abstract

“…In particular, the adaptation time is found to be similar to, but slightly greater than, that of the system of Henning et al (2008) and Pastoor et al (2008). In general, for a given noise level from the plant (w of Fig.…”

Section: Single Variable Implementationsmentioning

confidence: 65%

“…2.1). Alternative gradient estimation methods have also been suggested by Henning et al (2008) who used an extended Kalman filter, finding it to be much faster than the estimation of the standard algorithm. This algorithm was also tested by Wu et al (2015) who confirmed this result.…”

Section: Introductionmentioning

confidence: 99%

Extremum seeking to control the amplitude and frequency of a pulsed jet for bluff body drag reduction

2016

View full text Add to dashboard Cite

the aerodynamic drag. In all such situations, changing the properties of the flow may prove advantageous and can be achieved by flow control. In this paper, we show that a modified extremum seeking (ES) controller may be applied to a bluff-body wake to provide real-time optimisation of pulsed jet forcing for drag reduction.The wider topic of flow control is a broad one, but can be loosely split into passive or active and, in the latter case, open or closed-loop. While passive systems generally involve geometric modifications (see for example Park et al. 2006), active systems are those that require some energy input via an actuator. The nature of this input is either decided a priori for an open-loop system (e.g. Sipp 2012) or determined based on real-time measurements for a closed-loop system (e.g. Dahan et al. 2012). Closed-loop or feedback control is a mature research topic with a wealth of theory and methods available. The application of such methods to turbulent fluid flows has been a topic of research within the fluids community for some time (see for example Choi et al. 2008; Brunton and Noack 2015, for reviews), but generally has limited success in practice due to the difficulties in finding accurate models for the flow in question. The feedback control of many flows such as bluff-body wakes therefore remains a significant challenge.Many feedback control methods aim to force a system to track a reference trajectory or to maintain a demanded input in the presence of disturbances. For example, in autopilot flight control systems, the controller aims to maintain a constant heading and orientation in the face of atmospheric turbulence. Many such methods are based on a linear systems approach. However, in the context of fluid flows not only are the underlying dynamics nonlinear, but often the desired reference is not known a priori. Furthermore, both the model and "best" reference may change with time due Abstract Feedback control of fluid flows presents a challenging problem due to nonlinear dynamics and unknown optimal operating conditions. Extremum seeking control presents a suitable method for many flow control situations but involves its own challenges. In this paper, we provide a brief analysis of the extremum seeking method, with attention to modifications that we find to be advantageous. In particular, we present an adaptation for optimisation of the frequency of a harmonic input signal, a common scenario for open-loop flow control systems. We then present results from the experimental implementation of our modified method to the open-loop control system of Oxlade et al. (J Fluid Mech 770:305-318, 2015), an axisymmetric bluffbody wake, forced by a pulsed jet. We find that the system is able to achieve optimal operating conditions in both the amplitude and frequency of the harmonic input signal, and is able to largely reject the disturbances arising from measurements of a highly turbulent flow. We finally show the ability of the extremum seeking system to adapt to changing conditions.

show abstract

“…As the closed-loop bandwidth using an ESC is very low, methods to increase it are listed in [12]. In [13], we proposed using an Extended Kalman Filter to significantly speed up the single input case. An extension to the multiple input case can be found in [14].…”

Section: Introductionmentioning

confidence: 99%

Online Optimization Applied to a Shockless Explosion Combustor

et al. 2016

View full text Add to dashboard Cite

Abstract:Changing the combustion process of a gas turbine from a constant-pressure to a pressure-increasing approximate constant-volume combustion (aCVC) is one of the most promising ways to increase the efficiency of turbines in the future. In this paper, a newly proposed method to achieve such an aCVC is considered. The so-called shockless explosion combustion (SEC) uses auto-ignition and a fuel stratification to achieve a spatially homogeneous ignition. The homogeneity of the ignition can be adjusted by the mixing of fuel and air. A proper filling profile, however, also depends on changing parameters, such as temperature, that cannot be measured in detail due to the harsh conditions inside the combustion tube. Therefore, a closed-loop control is required to obtain an adequate injection profile and to reject such unknown disturbances. For this, an optimization problem is set up and a novel formulation of a discrete extremum seeking controller is presented. By approximating the cost function with a parabola, the first derivative and a Hessian matrix are estimated, allowing the controller to use Newton steps to converge to the optimal control trajectory. The controller is applied to an atmospheric test rig, where the auto-ignition process can be investigated for single ignitions. In the set-up, dimethyl ether is injected into a preheated air stream using a controlled proportional valve. Optical measurements are used to evaluate the auto-ignition process and to show that using the extremum seeking control approach, the homogeneity of the ignition process can be increased significantly.

show abstract

Extensions of adaptive slope-seeking for active flow control

Cited by 43 publications

References 32 publications

Stochastic modelling and feedback control of bistability in a turbulent bluff body wake

Stochastic modelling and feedback control of bistability in a turbulent bluff body wake

Extremum seeking to control the amplitude and frequency of a pulsed jet for bluff body drag reduction

Online Optimization Applied to a Shockless Explosion Combustor

Contact Info

Product

Resources

About